A244842 a(n) = (10^n - 1)*(10^n - 10)/90.

0, 99, 10989, 1109889, 111098889, 11110988889, 1111109888889, 111111098888889, 11111110988888889, 1111111109888888889, 111111111098888888889, 11111111110988888888889, 1111111111109888888888889, 111111111111098888888888889, 11111111111110988888888888889

Offset: 1

Author

Wesley Ivan Hurt, Jul 08 2014

Keywords

• nonn
• easy

Comments

For n > 1, the digit sums of a(n) are 18, 27, 36, ..., 9n (see example).

Examples

			-------------------------------------------------------
n    a(n)                    digitsum(a(n))    9*n
-------------------------------------------------------
2:   99                            18          9*2
3:   10989                         27          9*3
4:   1109889                       36          9*4
5:   111098889                     45          9*5
6:   11110988889                   54          9*6
7:   1111109888889                 63          9*7
8:   111111098888889               72          9*8
9:   11111110988888889             81          9*9
10:  1111111109888888889           90         9*10
11:  111111111098888888889         99         9*11
12:  11111111110988888888889      108         9*12, etc.
		

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..100
• Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).

Crossrefs

Cf. A053422, A109242.

Programs

Magma

[(10^n-1)*(10^n-10)/90: n in [1..15]];

Maple

A244842:=n->(10^n - 1)*(10^n - 10)/90: seq(A244842(n), n=1..15);

Mathematica

Table[(10^n - 1) (10^n - 10)/90, {n, 15}]

Formula

G.f.: -99*x / ( (x-1)*(100*x-1)*(10*x-1) ). - R. J. Mathar, Jul 11 2014

a(n) = 99*A109242(n-2). - R. J. Mathar, Jul 11 2014